ASTR 1000 Lecture Notes - Lecture 9: Black-Body Radiation, Emission Spectrum, Planetary Nebula
18 Jun 2018
School
Department
Course
Professor
Class 9 & 10
Radiation and Matter
Blackbody - is a theoretically ideal radiator and absorber of energy at all electromagnetic
wavelengths. The term comes from the fact that a cold blackbody appears visually black. The
energy emitted by a blackbody is called blackbody radiation. They come in the forms of: solids,
liquids, and dense gas. A THIN GAS does NOT act like a blackbody.
Applying heat to a blackbody
object, it will first start giving off
mostly red light, then red to orange,
then white (all the colours of the
spectrum)
“There is a relationship between
how much energy is coming off
and it’s temperatures”
Wien’s Law - relation between the wavelength at which a black body curve peaks and the
temperature of the emitter. The peak wavelength is inversely proportional to the temperature, so
the hotter the object, the bluer it's radiation. Allows you to look at an object in distance space and
work out the temperature of the object.
Stefan’s Law - relation that gives the total energy emitted per square centimetre on the surface
per second by an object of a given temperature. Stefan's law shows that the energy emitted
increases rapidly with an increase in temperature, proportional to the temperature raised to the
fourth power.
Temperature measures how fast the molecules are moving around – average speed of the
molecules.
Absolute Zero - when the molecules are not moving at
all.
find more resources at oneclass.com
find more resources at oneclass.com
find more resources at oneclass.com
find more resources at oneclass.com
!
Structure of Atoms
Atoms: have positively charged protons in the centre, surrounded by negatively charged
electrons. 90% of the atoms in the universe are hydrogen.
-Electrons will only absorb energy at certain amounts.
-Electrons have certain energy levels in atoms.
Absorption Line: dark line in an otherwise continuous bright spectrum, where light within one
narrow frequency range has been removed.
Emission Line: bright line in a specific location of the spectrum of radiating material,
corresponding to the emission of light at a certain frequency. A heating gas in a glass container
produces in emission lines in its spectrum.
Emission Spectrum: the pattern of spectral emission lines just bought an element. Each element
has its own unique in emission spectrum.
Neils Bohr: A Danish Physicist, he made foundational contributions to understanding atomic
structure and quantum theory
<— The difference between neighbouring energy’s getting
smaller and smaller because electrons act like a wave.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Blackbody - is a theoretically ideal radiator and absorber of energy at all electromagnetic wavelengths. The term comes from the fact that a cold blackbody appears visually black. The energy emitted by a blackbody is called blackbody radiation. They come in the forms of: solids, liquids, and dense gas. A thin gas does not act like a blackbody. Applying heat to a blackbody object, it will rst start giving off mostly red light, then red to orange, then white (all the colours of the spectrum) There is a relationship between how much energy is coming off and it"s temperatures . Wien"s law - relation between the wavelength at which a black body curve peaks and the temperature of the emitter. The peak wavelength is inversely proportional to the temperature, so the hotter the object, the bluer it"s radiation. Allows you to look at an object in distance space and work out the temperature of the object.
